JERUSALEM — Republican presidential candidate Mitt Romney vowed Sunday to stand with Israel against any threat from Iran, eager to show that he's a better friend than President Barack Obama.

“We must lead the effort to prevent Iran from building and possessing nuclear weapons capability,” Romney said. “We should employ any and all measures to dissuade the Iranian regime from its nuclear course. And it is our fervent hope that diplomatic and economic measures will do so. In the final analysis, of course, no option should be excluded. We recognize Israel's right to defend itself and that it is right for America to stand with you.”

He said the tough talk from a possible U.S. president is critical to let Iran's leaders know that they face unified and unrelenting opposition to their plans.

“Make no mistake, the ayatollahs in Iran are testing our moral defenses,” he said. “They want to know who will object and who will look the other way. We will not look away nor will our country ever look away from our passion and commitment to Israel.”

Romney did not specify any significant policy difference from Obama, who also refuses to rule out military action as a last resort.

But he drew an unspoken distinction with Obama, who has complained about open talk of warfare to stop Iran. Obama in March said there was “too much loose talk of war.”

“It is sometimes said that those who are the most committed to stopping the Iranian regime from securing nuclear weapons are reckless and provocative and inviting war,” Romney said. “The opposite is true. We are the true peacemakers.”

In a distraction from his message of the day, Romney had to back away from a statement from a top adviser promising support for unilateral Israeli military action against Iran.

“If Israel has to take action on its own, in order to stop Iran from developing that capability, the governor would respect that decision,” said Romney's senior foreign policy advisor Dan Senor.

Several hours later, the Romney campaign issued a clarification.

“Gov. Romney believes we should employ any and all measures to dissuade the Iranian regime from its nuclear course, and it is his fervent hope that diplomatic and economic measures will do so,” Senor said an email. “In the final analysis, of course, no option should be excluded. Gov. Romney recognizes Israel's right to defend itself, and that it is right for America to stand with it.”

In a move that surprised Israeli officials, Romney in his speech called Jerusalem the capital of Israel, telling the audience, “It is deeply moving to be in Jerusalem — the capital of Israel.”

The United States does not recognize Jerusalem as the capital, and the US embassy has remained in Tel Aviv despite repeated requests by Israel to move it to Jerusalem. The White House this week dodged questions about Israel's capital, mindful that the status is a major point of peace negotiations. Palestinian leaders maintain that East Jerusalem will be the capital of their future state and that the city is currently a “divided capital.”